Preparation

Melt butter in heavy large saucepan over
medium heat. Add leeks and potato; sauté
until leeks are slightly softened but not
brown, stirring often, about 5 minutes.
Add 3 cups broth; bring to boil. Reduce
heat, cover, and simmer until vegetables
are very tender, 10 to 12 minutes. Add
watercress and spinach; stir until wilted,
about 1 minute. Cool slightly.

Working with 1 cup at a time, puree
soup in blender until smooth. Transfer soup
to large bowl. Stir in lemon juice; season
with salt and pepper. Chill until cold, about
2 hours. Thin with more broth, if desired.

Ladle soup into bowls. Garnish center
of each with hard-boiled eggs and small
watercress sprigs.